The quarter-wave vertical — the simplest resonant antenna: how to size the element, and why it needs radials.
The most common vertical antenna is called a “quarter wave” vertical and gets its name as the length of the radiating element is ¼ wavelength long. This element is simply a rod or wire of this length in a vertical orientation.
This type of antenna needs what are called radials, which are wires arrayed around the bottom of the antenna, to act as the ground. Even if the antenna is sitting on the ground (which is common), these radials are required to obtain the proper performance. The general rule is that you want at least 8 radials, and they should be approximately half the length of the radiator or longer. Some recommend only needing 4 radials and making them 1.05x the element length (Dim A). In my opinion, more is better and if you have to choose between quantity and length, go for quantity.
| Dimension | Formula |
|---|---|
| A | = 234 / f |
| B | Varies - see above |
Note:
